This volume, tenth in the Yale Boswell Editions Research Series of correspondence, collects the letters exchanged between James Boswell (1740–1795) and Sir William Forbes of Pitsligo (1739–1806), eminent banker, civic improver, philanthropist, literary and cultural patron, and lay leader of Edinburgh’s ‘English Episcopal’ community. Forbes served Boswell as his most valued Scottish advisor, an affectionate and admired counsellor to whom he would often turn for personal, financial, moral, and religious guidance, and whom he would name executor of his estate and co-guardian of his children. Their friendship probably began in 1759 as new members of the same Masonic lodge in Edinburgh, and it deepened over time, and included their families. Boswell shared with Forbes significant portions of his private journal, and discussed with him his authorial ambitions as he developed the innovative biographical technique that would characterize his major publications on Samuel Johnson. He sought Forbes’s opinions about his original 1773 account of what would become his Journal of a Tour to the Hebrides, with Samuel Johnson (1785), and about his journal of his 1777 visit with Johnson at Ashbourne, later used in The Life of Samuel Johnson (1791). Boswell, in turn, broadened and enriched Forbes’s social range, providing a gateway into his remarkable circle of friends in London, in particular the members of the ‘Literary Club’. As Richard B. Sher explains in his introduction, none of Boswell’s other close friends straddled Boswell’s various worlds—his family life and professional career in Edinburgh, his lairdship of the Auchinleck estate in Ayrshire, his literary life in London—in this way. The volume, while thoroughly documenting the friendship that lies at its core, also illuminates the lives of Boswell and Forbes individually, especially Boswell’s final decade in London. It publishes a total of 111 comprehensively annotated letters, few of which have appeared previously in print: 79 exchanged between Forbes and Boswell between 1772 and 1794, and 32 involving other correspondents. The edition draws extensively on unpublished manuscripts in both the Boswell Collection at Yale and the Fettercairn Papers in the National Library of Scotland, including revealing letters from Forbes to his beloved wife ‘Betsy’, Lady Forbes, and to his close friend James Beattie, who would become Forbes’s own biographical subject in the decade after Boswell’s death.